1. Field of the Invention
The present invention relates to a rotary slide vane compressor, and more particularly, to a method for making a cylinder block of a rotary slide vane compressor in which the cylinder block body is made from an aluminum alloy material and split sleeves of ferrous material are inserted in the aluminum alloy body to strengthen the inner surface of the cylinder block.
2. Description of the Related Art
A rotary slide vane compressor comprises a cylinder block with an eccentric inner surface and a rotor having a plurality of radial vanes. The radial vanes moves radially outwardly to cooperate with the elliptical inner surface of the cylinder block. The outer end of the vanes are normally in slidable contact with the eccentric inner surface of the cylinder block.
This type of rotary slide vane compressor is used in many fields. In particular, such a rotary slide vane compressor is used for a refrigerating apparatus in an automobile. However, to mount a rotary slide vane compressor on an automobile, the compressor must have a light weight structure. One attempt was made to satisfy this requirement by forming the cylinder block of the compressor from an aluminum alloy material. An aluminum alloy cylinder block successfully realizes the object of a light weight structure, but brings other problems in that premature wear of the inner surface of the cylinder block occurs during the operation of the compressor, due to the properties peculiar to aluminum alloys, because the outer end of the vanes are normally in slidable contact with the eccentric inner surface of the cylinder block. The eccentric inner surface of the cylinder block is provided with an opening for an intake port, and wear of the inner surface is usually greatest in the region near that opening.
To solve this problem, it has been proposed to fit inner sleeve members of ferrous material in the aluminum alloy cylinder block. These inner sleeve members are separate members and located in the long diameter portions of the elliptical inner surface of the cylinder block, respectively, at the position therein of the intake port opening. These inner sleeve members are embedded in the aluminum alloy cylinder block by inserting the sleeve members in the mold during the process of casting the block.
A problem arises in the manufacturing of this structure by the insert casting process to embed the inner sleeve members in the block. The separate inner sleeve members are not bound together, and thus tend to be forced radially inwardly and out of position by the pressure of the poured molten metal (aluminum alloy). Therefore, after the casting process, the cylinder block with the offset inner sleeve members must be machine finished, resulting in an excessive cutting of the inner sleeve members. Accordingly, it is not possible to ensure that the inner sleeve members have a predetermined thickness on the inner surface of the cylinder block. To obtain inner sleeve members having a thickness sufficient to overcome the above problems, it is possible to prepare inner sleeve members having originally a greater thickness, but the greater the thickness of the inner sleeve member, the thinner is the thickness of the aluminum alloy cylinder block portion. This leads to an increase in the weight of the cylinder block because of the higher percentage of ferrous material therein, and reduces the strength of the block. Further, the difference of thermal expansion between the aluminum alloy and the ferrous material causes the formation of steps or a discontinuity in the inner surface of the cylinder block.